5). As observed, TNF-α and IL-6 mRNA levels (Fig. 5a,b) were also significantly
decreased following miR-155 inhibition. Although a decrease was observed Enzalutamide clinical trial for IL-1β (Fig. 5c), this effect was not statistically significant. As mRNA levels reflect cellular gene expression but not protein secretion, medium was collected from N9 cells following transfection with anti-miR-155 or control oligonucleotides and LPS treatment, and analysed by an ELISA to determine the levels of nine cytokines/chemokines expressed following microglia activation (Fig. 5d). This assay confirmed that miR-155 inhibition decreases the secretion of TNF-α and IL-6, but has no effect on IL-1β or any other of the tested cytokines, with the exception of TARC (thymus and activation regulated chemokine), whose levels although significantly lower compared with those of TNF-α and IL-6, were also found to be decreased. No significant differences were found between non-transfected NVP-LDE225 mouse N9 cells treated with LPS and cells transfected
with control oligonucleotides before LPS exposure (data not shown), which further confirms the specificity of the effects observed with the anti-miR-155 oligonucleotides. Taken together, these results indicate that miR-155 can act as a strong inducer of cytokine production following microglia activation and that miR-155 inhibition decreases both the expression and the secretion of specific pro-inflammatory cytokines. Nitric oxide is an inflammatory mediator whose production by iNOS is a well-described hallmark of microglia activation. Although NO is a volatile gas, it is possible to monitor
its release to the cell culture isometheptene medium by measuring the levels of nitrites, the sub-products of NO oxidation, through the Griess reaction. Aiming at assessing the contribution of miR-155 for NO production, N9 microglia cells were transfected with anti-miR155 oligonucleotides or a plasmid encoding miR-155, before LPS treatment (0·1 μg/ml for 18 hr). As expected, cells exposed to LPS presented a strong increase in nitrite production (Fig. 5a). However, miR-155 inhibition before LPS treatment led to a significant decrease in nitrite release to the medium (40%), with respect to LPS-treated untransfected cells, whereas miR-155 over-expression had the opposite effect, increasing nitrite levels. These results could not be reproduced using a control oligonucleotide or a control plasmid, which indicates that the changes in NO and nitrite production are a specific response to miR-155 modulation. Moreover, a decrease in iNOS mRNA, as assessed by qRT-PCR (Fig. 6b), and in protein levels, as assessed by Western blot (Fig. 5c,d), was observed following miR-155 inhibition, but not following transfection with the control oligonucleotides. Western blot analysis also showed an increase in iNOS levels after miR-155 over-expression, which further confirms the contribution of miR-155 to the regulation of NO synthesis by modulating iNOS expression.